1. Field of the Invention
The present invention relates to a simple remote control device which uses the public telephone network as a transmission medium.
2. Description of the Prior Art
In addition to radio remote control devices, several remote control installations using telephone lines are known, in particular those described in the following documents: US-A-4 206 444, GB-B-1 235 481, FR-A-2 074 678 and FR-A-2 138 217.
U.S. Pat. No. A-4,206,444 relates more particularly to a computer power-supply control which even requires a special telephone line. For this reason, this device is intended for a different purpose from that covered by the present invention.
The object of the device described in British Patent B-1 235 481 also differs from that of the present invention. Moreover, its design and its mode of operation are liable to produce many interfering harmonic vibrations which risk giving rise to incorrect commands.
The documents FR-A-2 074 678 and FR-A-2 138 217 have disclosed remote control devices which use the telephone network as a transmission medium and which make it possible to transmit signals in both directions between two stations. However, these devices, the first of which incorporates a manual reversing key, have a design tending to produce harmonic vibrations which risk giving rise to incorrect commands. Moreover, the system for coding the instructions is such that the least distortion of the message results in an incorrect interpretation of the instruction. This type of device is therefore unsuitable for uses where high operating reliability is required.
Centralized remote control devices are also known which use the high-voltage and low-voltage network as a transmission medium. Because of their operating principle and their basis of construction, these devices do not allow signals to be transmitted in the opposite direction.
It is therefore established that there is a need for providing remote control devices which work with good operating reliability to allow uses, such as, for example, the remote control of valves or circuit-breakers, whilst using a public telephone line. The aim is, therefore, to avoid the need to use one or more private or special telephone lines intended for the transfer of complex and numerous data, such as, for example, an interconnection between computers.